1.(1) Development of the Zupancic magnetic resonance imaging coil and the electron spin resonance imaging (ESRI) apparatus adopting dielectric resonator.(2) By using these apparatus, the observation of the ferroelasstic domain structure has been studied.2.(1) Development of apparatuses, applying heat and uniaxial stress, for STM and AFM.(2) By using this apparatuses, the temperature dependence of ferroelastic domain and domain boundary structure of EuP_5O_<14> and GdP_5O_<14> obtained by STM and AFM and X-ray diffraction was observed. We observed the temperature dependence of monoclinic beta angles and analyzed the width (about 0.6 mu m) and zigzag structure of ferroelastic domain boundary.(3) According to Sapriel's ferroelastic theory which doesn't take into consideration the width of the domain boundary, LaNbO_4 should have incomennsurate (W') twin boundaries, but W' boundaries cannot be detected through our close analysis of neutron and X-ray diffractions. Therefore if the incommensurate twin boundaries are suposed to exist, they are thought to be dissolved in the domain boundary regions.